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Ancient dwarf galaxy was heavy-element factory

Cataclysm in Reticulum II identified as site of ‘r-process’

HEAVY METALS Scientists observed nine stars (circled) in the dwarf galaxy Reticulum II. Their data (shown for three stars) indicated the presence of heavy elements, formed through a sequence of reactions known as the “r-process.”

A. Ji, Fermilab/Dark Energy Survey (background image)

SALT LAKE CITY — In the primeval universe, a violent event roiled a dwarf galaxy, leaving an indelible mark on the stars that formed there. Scientists reached that conclusion after finding traces of heavy elements produced by the cataclysm in the ancient dwarf galaxy Reticulum II.

“It might be the first time where we can distinctly point to something and say, ‘One thing happened in this galaxy 13 billion years ago,’” says Alexander Ji of MIT, who presented the research April 19 at a meeting of the American Physical Society.

Many of the universe’s heaviest elements form primarily through the r-process, a chain of reactions through which atomic nuclei climb the periodic table, swallowing up neutrons and decaying radioactively. But scientists don’t agree on where the seeds of these heavy elements are sown, except that it must be an environment rich in

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